1. Field of the Invention
The present invention relates to a dot head for driving the needle of a wire dot printer and a method of manufacturing the armature structure for the dot head.
2. Description of the Related Art
The wire dot printer is arranged to move a printing wire (hereinafter, simply referred to as a wire) called a needle forward and backward to strike the tip end of the wire against a print medium thereby to print a dot-shaped image thereon. Since the wire dot printer employs such the printing method, the wire dot printer can simultaneously print plural slips etc. in a stacked state and so is employed for business use. Although there are various kinds of methods as the printing method of moving the wire (needle) forward and backward, the method called a clapper type is generally employed. The clapper type has been employed widely since the structure thereof is simple and a relatively large stroke can be secured. Such the kind of the printing method is proposed by JP-A-2005-75000, for example.
The dot head of such the clapper type includes an armature for driving a wire backward and forward. The armature is pivotally supported at a portion near the one end thereof so as to be rotatable. The armature is provided with an absorbed portion opposing to a core, at the intermediate portion between the pivotally supported portion and the free end of the armature. An arm is extended from the free end of the armature so as to be integrated with the armature. A needle for printing is provided at the tip end of the arm. The needle is attached to the arm in a manner that the axial direction of the needle crosses with the longitudinal direction of the arm at the tip end of the arm. The armature and the arm integrally provided with the armature rotate in the operation direction around the pivotally supported portion when the absorbed portion is absorbed by the magnetic force generated by the core. When the armature and the arm integrally provided with the armature rotate in the operation direction in this manner, the needle provided at the tip end of the arm move forward. In contrast, when the magnetic force having been generated by the core disappears, the armature and the arm integrally provided with the armature rotate in the restoring direction by a spring force etc. and so the needle move backward.
The dot head is arranged in a manner that a plurality of the armatures each thus configured are disposed radially around a print portion.
As described above, the armature integrally provided with the arm moves the needle forward and backward at a high speed for many times in response to the magnetic field. In order to attain such the function, the armature is required to be formed by material with a high magnetic permeability and excellent durability. Conventionally, pure iron is widely used as the material of the armature. Since the pure iron is relatively soft, the pure iron is subjected to the carburization processing thereby to increase the strength thereof. However, it is very troublesome to subject the pure iron to the carburization processing, and the pure iron having been subjected to the carburization processing leaves much to be improved in efficiency such as a magnetic permeability and durability.